fixes hasOne relation url generation for nested resources

The scope interface was modified:
* the $fetchUrlFor method is added to provide nested resource's fetch url
* the $collectionUrl method is added to provide nested collection url

closes #42

Breaks update url for hasOne relation on non anonymous resources being nested
if resource wasn't identified. An anonymous resource should be used for that effect.
fixes hasMany relation not reseting collection contents on inline content

closes #40
refactor($restmod): overlapping resource requests are chained instead of being run in parallel.

Also, ModelCollection.$reset will now cancel any ongoing requests.

closes #38
fixes(DebouncedModel): promise handling now works ok with new chained request structure.